Honeycomb battery structure

ABSTRACT

A battery construction and a method of producing the construction. The construction comprises a ceramic separator having a honeycomb structure in which cells run lengthwise of the honeycomb and are separated by porous walls, and internal positive and negative electrodes positioned in part at least within the honeycomb structure.

This application claims the benefit of U.S. Provisional application Ser.No. 60/005,207, filed Oct. 11, 1995, entitled HONEYCOMB BATTERYSTRUCTURE, by George E. Berkey, John L. Stempin, Ronald L. Stewart andDale R. Wexell.

RELATED APPLICATIONS

Applications entitled BATTERY SEPARATOR and HONEYCOMB BATTERY SEPARATOR,filed Jun. 19, 1995 and Jul. 26, 1995 under Ser. No. 08/491,766 and Ser.No. 08/506,713, respectively now U.S. Pat. Nos. 5,514,494 and 5,554,464.The first application is directed to a rigid, porous, ceramic batteryseparator having a porosity of 40-90%, a pore size of 0.1-25 microns, athickness of 1-12 mm and resistance to acid attack. The secondapplication is directed to an elongated, rigid, porous, ceramicseparator for a battery, the separator having a honeycomb structure inwhich open cells are separated from adjacent cells by thin, porous,ceramic walls, the cell walls being porous and the open cells and wallpores being adapted to be filled with an electrolyte.

1. Field of the Invention

Separators of honeycomb structure for a metal-electrolyte-metal battery.

2. Background of the Invention

The oldest and best known type of rechargeable battery is the lead-acidbattery. While the present invention is not so limited, it has beendeveloped as an improved lead-acid type battery. Accordingly, thedescription is primarily in terms of such a battery.

A typical lead-acid battery comprises a positive electrode, a negativeelectrode, one or more separators, and an electrolyte. The electrodesfunction both as electrical contacts and as mechanical load-bearingelements. Each electrode is formed by coating a lead or lead alloy gridwith an active paste material. The paste dries to form a porous layer ofthe active material as part of each electrode.

A separator may be any porous, perforated, or fibrous material thatsufficiently isolates the electrodes to prevent short circuiting.However, the separator must also be sufficiently open to permit iontransfer through the electrolyte contained in the separator. Perforatedplastic, or glass fiber, sheets are commonly used as separators. Acompressed mat of glass fibers is currently used in many commercialstorage batteries.

Porous earthenware and sintered silicate sheets have also been proposed.However, they have not been adopted commercially to any significantextent. One problem has been lack of sufficient porosity to permitproper operation of a battery.

The electrolyte may be any ionic medium that can provide ion transferbetween the electrodes. In a lead-acid battery, sulfuric acid is theelectrolyte employed.

A battery may be packaged in a plastic case for insulating purposes.However, the electrodes constitute the primary mechanical support andload-bearing means in current storage battery construction.

The glass fiber mat, now in use as a separator, has certain desirablefeatures. It readily takes up and holds electrolyte, a property commonlyreferred to as wettability or wickability. It is also resistant toattack by the electrolyte, and provides acceptable electricalproperties.

The fiber mat separator is, however, flexible and lacking in mechanicalstrength. This means that the electrodes, the casing, or other supportmembers must be the primary source of structural integrity in a battery.

Batteries are commonly classified as either a flooded type or a starved,or sealed, type. In both types, the electrodes are in contact with theseparator and held in that assembly. The porous, active material coatingon the metal grids, as well as the separator, become saturated withelectrolyte. In the flooded type, the electrode and separator assemblyis immersed in excess electrolyte so that the open space around theassembly is filled with electrolyte, e.g. sulfuric acid. In the starved,or sealed, type, the electrolyte is completely contained within thepores of the separator and electrode paste. In this construction, it isimportant that the electrolyte be retained in the pores to avoid leakageof the corrosive acid electrolyte.

U.S. Pat. No. 5,554,464 describes a rechargeable battery assemblycomprising an elongated, rigid, porous, ceramic separator. The separatorhas a honeycomb structure in which open cells are separated fromadjacent cells by thin, porous, ceramic walls, the open cells andseparating walls running lengthwise of the honeycomb separator. The cellwalls are porous, and the open cells and wall pores are available to befilled with an electrolyte to permit ion flow between electrodes in abattery. In this assembly, electrodes are applied externally, that is,to the side walls of the separator.

The present invention is also based on a battery assembly employing aporous, ceramic, honeycomb body as a separator. In the present battery,however, electrodes are assembled internally, that is, within the cellsof the honeycomb body.

SUMMARY OF THE INVENTION

The invention resides in part in a battery construction comprising aceramic separator having a honeycomb structure in which cells runlengthwise of the honeycomb and are separated by porous walls, andinternal positive and negative electrodes positioned in part at leastwithin the honeycomb structure.

It further resides in a method of producing the battery constructionwhich comprises forming an extrudable mixture of ceramic materialprecursors, extruding the mixture through a die designed to produce anelongated body having open cells running lengthwise of the body withthin walls defining and separating the cells, cutting the separator fromthe extruded, elongated body, introducing active material into selectedcells and positioning an electrode wire in each cell.

PRIOR ART

Prior art known to Applicants and deemed relevant is suppliedseparately.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a perspective view of a square, ceramic, honeycomb body.

FIG. 2 is a top plan view of the body of FIG. 1.

FIG. 3 is a cross-sectional view taken vertically downward from one faceof the body of FIG. 1.

FIG. 4 is a view similar to FIG. 3 but taken vertically up from theopposite face of the body of FIG. 1.

FIGS. 5, 6 and 7 are top plan views of honeycomb bodies illustratingdifferent cell patterns in accordance with the invention.

DESCRIPTION OF THE INVENTION

The present invention, like that of our second related patent, adoptsprior honeycomb production technology. In particular, it adoptshoneycomb structures and production features from the art of ceramicsubstrates designed for catalytic converters used in treating exhaustgases.

The term "honeycomb" has come to mean cellular, extruded, porous bodiesregardless of cell shape. Thus, the cells are not restricted to theconventional hexagonal shape, but may have any desired cross-sectionalgeometry such as oval, round, rectangular, square, and triangular.

Honeycomb substrates for catalytic converters are extruded incontinuous, elongated bodies sometimes referred to as logs. These bodiesmay also be extruded in any desired cross-sectional geometry, such as,oval, round, rectangular, square and triangular.

The extruded bodies are customarily composed of open cells running thelength of the log. The cells are separated and defined by thin, porouswalls. Cell sizes may vary from 2 to 2300 cells/6.25 sq. cm. (sq.") ofopen face. For present purposes, no more than about 100 cells/6.25 sq.cm. are practical to permit introduction of wires and active material asdescribed subsequently. The cells are usually of uniform size, but maybe of variable size and/or shape depending on the extrusion die pattern.

The invention is based on two functional concepts for using an extrudedhoneycomb substrate as a battery separator. The first concept involvesemploying the separator as the essential supporting structure for abattery cell. The second concept involves assembling wires internally inhoneycomb cells to function as electrodes. These concepts may beembodied in a number of different assemblies. Some typical examples areillustrated in the accompanying drawings as described hereafter.

FIG. 1 is a perspective view of a square, ceramic, honeycomb body 10having 64 open cells as extruded. Body 10 is produced in conventionalmanner by extruding a batch of suitable composition through a square diesuch as disclosed in U.S. Pat. No. 3,905,743 (Bagley). It will beappreciated that extrusion dies can be constructed to produce almostlimitless different cross-sectional shapes. Cylindrical or oval bodiesare commonly extruded for catalytic converter use. For present purposes,we have used square or rectangular bodies for larger size batteries, andround bodies for small assemblies such as C batteries.

FIG. 2 is a top plan view of body 10 showing the upper face 12 thereof.Face 12 has a preferred arrangement of equal size cells with walls ofuniform thickness. If necessary, dies can be produced to provide bodieshaving non-uniform cell and/or wall dimensions.

Body 10 contains open channels, or cells, 14 that run the length of body10. Cells 14 are of uniform size throughout their length. For presentpurposes, cells 14 have a common size, that is, provide areal openingsof equal size. The size is generally defined in terms of cells per unitarea, and is dependent on the requirements of the battery applicationinvolved.

Cells 14 are defined by thin walls 16 which surround each cell andseparate it from adjacent cells in the honeycomb. The thickness of wall16 may be varied depending on the extrusion die employed, the nature ofthe batch extruded, and the rate of extrusion.

In general, wall thickness decreases as the numbers of cells per unitarea increase. A major factor to consider is structural integrity, thatis, the fragility of the structure. As a general rule, cell size andwall thickness are relatively uniform throughout a body. This providesimproved battery performance as well as convenience in production. Wallthickness may vary from about 1.5 mm. (1/16"), in the case of a fewcells per unit area, down to about 0.12-0.25 mm. (5-10 mils), in thecase of a honeycomb with a hundred cells per unit area.

Batteries with electrodes mounted internally in a honeycomb separatormay be assembled in a variety of ways. A primary consideration is thatany electrical leakage between the positive and negative electrodes,including the active coatings associated therewith, must be avoided.Another major consideration is that the porosity in the separator besufficient to contain the electrolyte and permit ionic flow between theelectrodes.

FIGS. 3 and 4 illustrate one manner of assembly. FIG. 3 is across-sectional view taken vertically down from face 12 through body 10.It shows the body after initial processing to produce the battery anode.FIG. 4 is a similar view illustrating cathode production.

The first step in carrying out the assembly is to close off selectedcells 18 on face 12 of body 10. One row of cells around the periphery ofthe body will be closed, as will alternate cells within the interior ofthis periphery row of cells. The sealing material 20 employed to sealoff cells 18 extends inwardly in each sealed off cell a short distancefrom face 12. Its extent is shown by a dotted area in each cell in FIG.3.

The next step is to insert wires 22 of appropriate size and compositioninto each of unfilled cells 24. Wires 22 may be lead-containing,conducting wires that extend the length of the cell. They also extendsome distance out from face 12 to permit making electrical contact.Wires 22 collectively become the positive electrode of the battery.

A mixture of lead oxide and free lead powder 26 is now introduced intounfilled cells 24 around wires 22. Vibration can be used to assistintroducing the powder into the cells. The cells will be only partiallyfilled to allow for expansion when an electrolyte, such as sulfuricacid, is introduced. This forms a paste which functions as the activematerial for each wire electrode. A feature of the inventiveconstruction is optimum utilization, and confinement during service, ofactive material.

The open cells 24 are now sealed off and the several wires 22 areintegrated to form a terminal. One procedure is to cover face 12 with alayer of polymer that forms a rigid coating with wires 22 protruding.The wires may then be soldered together, or otherwise integrated, toform a single positive terminal.

Alternatively, wires 22 may be such as to protrude only a short distanceabove face 12. In that case, face 12 is dipped into molten lead, orotherwise provided with a lead coating. This simultaneously formscontact with each wire electrode 22 to form a unified anode terminal 28.

The procedure just described is now reversed to form a negativeelectrode for the battery assembly. This is described with reference toFIG. 4 which is substantially similar to FIG. 3. FIG. 4 shows theopposite face 30 of honeycomb body 10. Each cell 18, which remainsunfilled on face 12, is now filled on face 30. This isolates wires 22from possible contact with the cathode being formed on face 30.

Cells 18 that were closed off on face 22 are left open on face 30,except for the peripheral row of cells. Wires 32 are positioned in cells18 in the same manner as wires 22 were positioned in cells 24. Thepowder mixture 26 containing lead, and an acid electrolyte, areintroduced around each of wires 32 to form the negative active material.Again, wires 32 protrude sufficiently beyond face 30 to permitintegrating into a terminal, in this case the negative terminal orcathode. Face 30 is then sealed off, and wires 32 are integrated, asbefore. This may be as described with reference to FIG. 3, that is, by aplastic coating plus soldering of the wires, or by applying a leadcoating.

When faces 12 and 30 are sealed off, the outside of body 10 should beporous to prevent possible pressure buildup during battery operation. Itwill also be appreciated that the sealing off of cells 18 and 24 couldmore conveniently be carried out prior to introducing wires and powderat either face. Also, in the charging process, PbO is oxidized to PbO₂at the cathode and reduced to Pb at the anode. Accordingly, the initialcharging step might be eliminated, or at least shortened, by introducingPbO₂ powder around wires 22 and lead powder about wires 32.

The introduction of powdered material into the cells can be a verytedious operation, particularly where small cells are involved.Accordingly, an alternative method has been devised. In this alternativemethod, a closed end, tubular member of smaller OD than cell diameter isprovided with a pattern of holes along its sides. An active materialpaste of suitable viscosity for application is prepared. The tubularmember is filled with this paste. The tube is then inserted into a celland air pressure applied to the open end of the tube. This extrudespaste into the cell, thereby coating the cell walls. Removal of the tubethen leaves the walls coated with a layer of paste. This eliminates theproblems with non-uniformity in filling with dry powder. It also aids inproperly centering the electrode wires in the cells.

A lead/antimony alloy wire provides the necessary stiffness to permitease of handling the wire. Wire size, cell size, and the resultantvolume ratio of electrode wire to active material in a cell will varydepending on requirements of a particular application. Wire size shouldbe large for a deep discharge battery, and fine for high powerapplications. With wires inserted in the coated cells, the honeycombfaces are then sealed off, as described above, by a plastic or leadcoating.

The appropriate ratio of acid to electrode material is critical toproper operation of a lead-acid battery. Sufficient excess acid must bepresent to permit ready availability of hydrogen ions at the cathode. Aceramic honeycomb battery structure may be utilized to provide areservoir of acid electrolyte. This reservoir supplies acid to theindividual electrode cells as necessary through the porous walls. Sometypical cell arrangements for this purpose are now described .

FIG. 5 illustrates one of the numerous pattern variations that arepossible in utilizing a honeycomb body in accordance with the presentinvention. FIG. 5 is a top plan view of one face of an assembly 50 suchas described in FIGS. 3 and 4. Each square in face 52 of assembly 50represents a cell 54 that runs lengthwise of the honeycomb body. Thelines represent cell walls. A feature of this assembly is that the cellsmarked A represent electrolyte reservoirs. Thus, to the extent thatelectrolyte may be expended, an internal reservoir is provided. Thecells marked C will have electrode assemblies produced therein.

FIG. 6 is also a top plan view of face 62 of an assembly 60. Itillustrates still another useful pattern of cells 64. This pattern isparticularly useful where one face of the body is completely sealed off,and both the anode and cathode terminals are formed on the oppositeface. In pattern 60, cells 64 having anode or cathode wires inserted aredesignated by C. Cells 64 are arranged in rows with the spaces 66between any two rows functioning as reservoirs.

With the active cells arranged in rows, the production of anode andcathode terminals may be simplified. Thus, either an anode or cathodeterminal may be formed by applying a conductive layer along a row ofcells. For example, a conductive layer might be applied over eachvertical row of active cells in the arrangement of FIG. 6. Necessarily,all of the cells in any row so bridged will have a common sign, that is,all positive or all negative electrodes.

The assemblies and cell arrangements shown above have utilized a squarehoneycomb configuration with square cells. However, it should beappreciated that other honeycomb configurations, such as round, oval, ortriangular may be employed. These may have cells of square, or othergeometric, design depending on the die employed to extrude thehoneycomb.

For example, a cylindrical honeycomb body may have annular cellssubdivided as desired. FIG. 7 is a top plan view of face 72 of anassembly 70. It shows such a pattern wherein the annular cells 74 aresubdivided into quarters. As in FIGS. 5 and 6, acid reservoirs, that isopen cells, are shown as A and electrode cells as C. Positive wires andnegative wires may extend from opposite faces as illustrated in FIGS. 3and 4. Alternatively, both may extend from one face as illustrated inFIGS. 5 and 6.

It will be appreciated that numerous variations within the scope of theinvention are contemplated. While the invention has been described interms of sealed batteries, it is also possible to achieve benefits inflooded cell batteries as well. Also, the invention permits variousunconventional battery configurations, such as a U-shaped battery.

We claim:
 1. A battery construction comprising a ceramic separatorhaving a honeycomb structure with two opposed faces between which cellsrun lengthwise of the honeycomb and are separated by porous walls, atleast a portion of the cells having internal positive and negativeelectrodes positioned in part at least within the honeycomb structureand a portion of each such cell having sealing material that extendsinwardly from a face of the structure and an electrode member of smallerdiameter than the cell extending into the cell from the opposite face.2. A battery construction in accordance with claim 1 wherein selectedcells in the honeycomb structure are at least partially filled withactive material around an electrode extending into each selected cell.3. A battery construction in accordance with claim 2 wherein walls onthe selected cells have a coating of active material and an electrodeextending into the cell within the wall coating.
 4. A battery inaccordance with claim 2 wherein the electrode, the active material andan electrolyte substantially fill a cell.
 5. A battery construction inaccordance with claim 1 wherein a first selected group of cells has asealing material extending inwardly into the cells from a first face ofthe honeycomb and an electrode extending into each sealed off cell fromthe opposite face.
 6. A battery construction in accordance with claim 5wherein a second set of cells, exclusive of the first set, has a sealingmaterial extending inwardly into the cells from the opposite face and anelectrode extending inwardly into each of said second set of cells fromthe first face.
 7. A battery construction in accordance with claim 6wherein each set of electrodes protrude from its respective face, and anelectrically conductive layer covers each set, thereby forming positiveand negative terminals.
 8. A battery construction in accordance withclaim 6 wherein each set of electrode wires protrudes from itsrespective face, an electrically insulating layer surrounds theprotruding electrodes on each face, and each set of electrodes isintegrally joined to form positive and negative terminals.
 9. A batteryconstruction in accordance with claim 1 wherein one face of thehoneycomb structure is sealed off, electrodes are inserted in selectedcells from the opposite face, and alternating electrodes are connectedto form a positive terminal and the remaining electrodes are connectedto form a negative terminal.
 10. A battery construction in accordancewith claim 1 wherein selected cells are open to provide electrolytereservoirs.
 11. A battery construction in accordance with claim 1wherein the porosity in the wall sections of the separator is over 40%by volume, the wall thickness between electrodes is at least 0.12 mm andthe honeycomb has 2-100 cells per square inch.
 12. A batteryconstruction in accordance with claim 1 wherein the ceramic separator isselected from the group composed of silica, alumina, mullite andmixtures thereof.